It is commonly known to make tubes with internal fins for improving the heat transfer characteristics of the tubes and also for other applications. Such fins normally have rectangular profiles. However, the rectangular profile does not always provide an acceptable profile and it is often necessary to reform the fins to more suitable configurations. For example, one particular application is the making of an electric motor commutator wherein a finned tube section together with a shaft bushing is placed in a mold and plastic material forced between the shaft bushing and the tube under heat and pressure to anchor the fins into the plastic material. The tube is thereafter cut longitudinally between the fins to electrically insulate the commutator bars from each other. It has been common practice to provide the fins with various projections or to deform the fins to provide an anchor to prevent loosening of the commutator bars, especially in modern high speed universal motors wherein the commutator bars are subjected to very high centrifugal forces. One particular method of reforming the fins is disclosed in U.S. Pat. No. 3,987,539 granted Oct. 26, 1976. In the patent, a mandrel is used having on its outer surface a number of forming surfaces which change progressively from a sharp profile at the front or leading end of the mandrel to a substantially flat profile at the rear or trailing end. The reforming operation is performed on individual commutator tubes of short length (a few times the length of the final commutator). With the above method, the short commutator tubes require a very high degree of dimensional tolerance stability to reform the rectangular fin tip properly, otherwise a large number of rejects occurs.